1. Field of the Invention
This invention relates to a modular spool with a bore therethrough having a removable valve package positioned in the bore. This “intervention spool” eliminates the need for a separate subsea test tree and provides a bore equal in diameter to the blowout preventer stack positioned above. The intervention spool can be used in various forms for performing the functions of other well control components.
The installation of subsea trees for control of oil and gas well production requires the installation of down hole completion equipment that is suspended in a wellhead body or housing at the sea floor. The well is then tested by “unloading”, i .e., the well is allowed to flow unimpeded up a riser string to a test separator on a drilling unit at the surface. This drilling unit may take the form of a mobile offshore drilling unit (“MODU”) or rig or other type of hull based vessel as a spar or tension leg platform.
It is important that well control be maintained under these circumstances. This well control requires the ability to shut off flow to the surface and provide for a disconnect capability should disconnection of the mobile offshore drilling unit be necessary. The current approach to this need is to utilize a subsea test tree that is an adaptation of a valve package typically used during well appraisal drill stem testing. These subsea test tree designs are self-contained valving arrangements including valves with actuators that are used as part of the running or landing string for the tubing hanger. Such subsea test trees have a number of limitations including the size of the valves, the pressure rating of the valves, the temperature rating of the actuators and valves, the force available for shearing and actuation under high pressure and the allowable minimum internal diameter of the drilling riser.
A solution that eliminates the actuation system from the valve package in its running mode and mounts the actuators on the side of a spool or similar is very desirable to overcome these limitations. Such an intervention spool design allows the valve size to be maximized for a given riser internal diameter, allows the use of sufficiently large actuators for required pressure and shearing forces, allows the actuator components to be removed from the high pressure and high temperature environments and allows control of the valves by a control system external to the riser.
2. Description of Related Art
U.S. Pat. No. 5,372,199 to E. J. Cegielski et al. shows a subsea wellhead in which the production string or the production tree may be removed independently of the other.
A wellhead having a spool tree mounted above the wellhead in place of a conventional Christmas tree is disclosed in U.S. Pat. No. 5,544,707 to H. P. Hopper et al.
International Patent Application Number WO 99/18329 to FMC Corporation shows a slimbore completion system that utilizes a reduced diameter tubing hanger which is arranged and dimensioned to pass through the bore of the riser and blowout preventer.
A wellhead assembly in which an in-line tree with a vertical production bore is landed within a wellhead housing is disclosed in U.S. Pat. No. 5,992,527 to D. Garnham et al.
U.S. Pat. No. 6,039,119 to H. P. Hopper et al. shows a completion system with a spool tree in which a tubing hanger is landed at a predetermined angular orientation and allows monitoring of the production casing annulus pressure.